This invention relates generally to reciprocatory machines, including those operable as internal combustion engines, but in a particularly preferred embodiment relates to an improved sleeve valved engine.
In recent decades, substantial research effort has been expended on a quest for a commercially practical adiabatic engine. A useful reference on the topic is xe2x80x9cThe Adiabatic Enginexe2x80x9d, published by the Society of Automotive Engineers (SAE) in 1984 as part of its Progress in Technology Series (No. 28). Most of the uncooled adiabatic engines produced for research purposes under various programs made extensive use of ceramic insulation inserts as, for example, cylinder and combustion chamber liners, piston caps, headface plates, valve seats, valve housings and valve guides. These programs generally examined the feasibility of ceramic lined adiabatic engines, and yttria partially-stabilised zirconia (PSZ) was considered to be a particularly promising ceramic for the purpose. The research programs contributed significantly to advanced engine design, but the reality is that there is today no successful adiabatic production engine. The principal problems encountered have included a short ceramic life, an inability to identify lubricants which performed satisfactorily at the high temperatures involved, an inability to obtain greater expansion energy within the cylinder and hence the need to extract energy from the exhaust gases by secondary expansion. A further problem was the substantial decrease in volumetric cylinder efficiency due to the heating effect of hot cylinder/combustion chamber surfaces on the incoming air charge.
Several contributors to the above cited publication, including GM, Cummins and Komatsu, conclude that it is not possible to achieve practical adiabatic engine operation without high exhaust gas temperatures, turbo-charging or super charging (preferably with intercooling) and secondary expanders. A design by Kirloskar relied on vertically aligned cylinder fins and air cooling by convection, but achieved only a low level of adiabatic operation.
At a somewhat earlier time, the use of heat-insulated members adjacent to the combustion space was proposed by Sir Harry Ricardo for several purposes in enhancing the performance of high speed engines. In his classic text, xe2x80x9cThe High Speed Internal-Combustion Enginexe2x80x9d, Fourth Ed 1953 (Blackie and Son Glasgow), Ricardo suggests the use of a heat-insulated member placed well out of the path of the entering air. He suggests that such a member would be easy to provide for in a compression swirl engine, and possibly in an induction swirl engine, of either the sleeve valve 4-stroke or the 2-stroke type, but could only be fitted with great difficulty, or with breathing restrictions, in an open chamber poppet valve 4-stroke engine. The heat-insulated member is said by Ricardo (at page 26 of the aforementioned text) to serve the functions of raising the compression temperature without reducing the density and, if suitably positioned and proportioned, to keep the delay period constant in terms of crank angle, thus allowing a fixed time of injection throughout the entire speed range. Ricardo further suggests that the heat-insulated member would also be useful because its surface temperature will be high enough to prevent the deposition of carbon or ash, and if so placed that the jet of fuel impinges upon it, it will eliminate completely the building-up of deposits in this zone, particularly when using high ash content fuels.
In Ricardo""s textbook, there is also discussion, at pages 102-115, of a heat-insulated member in the context of compression swirl compression chambers. A particular form is illustrated in FIG. 7.13 by way of an annular heat-insulated lining for the combustion chamber wall, in the context of a sleeve-valve combustion chamber. In respects other than the presence of the lining, this illustration is typical of sleeve valved compression-ignition engines, in that the combustion chamber was formed in the so called junkhead by a cylindrical wall substantially smaller in diameter than the main cylinder wall guiding the piston and the valve sleeve. The arrangement illustrated in FIG. 7.13 of the Ricardo text would not be practical, however, since differential expansion between the junkhead body and the liner could be expected to cause practical difficulties as operating temperatures varied, leading to sealing and/or mechanical and/or fatigue failures. A loss of heat insulation would then result, due to the annular space filling with soot and/or carbonised oil.
In sleeve-valved compression ignition engines, the sleeves typically oscillated both longitudinally and circumferentially and a common feature of the engines was admission of the air in a manner which generated a high speed revolving swirl of the air in the chamber, thus enhancing mixing and combustion. Sir Harry Ricardo described typical swirl ratios for 4-stroke operation (ie. swirl RPM relative to crankshaft RPM), for highest brake mean effective pressure and lowest brake specific fuel consumption, of the order of 10.
Ricardo also developed a series of indirect injection combustion chambers, illustrated for example in his aforementioned text at FIGS. 7.7 and 7.10. Engines of similar type are disclosed in British Patent 1046104, in Japanese patent publication 62-051718 and German patent publication 1476351. These indirect injection systems involved localized swirls at the transit passage into the main chamber.
Engines having co-axial combustion chambers smaller than the main chamber are disclosed in U.S. Pat. Nos. 3,815,566 and 5,778,849, and in Japanese patent 5-157002. In U.S. Pat. No. 3,815,566, a perforated baffle separates the chambers.
It is an object of the invention to provide an internal combustion engine of enhanced thermal efficiency, and in one or more embodiments, to provide an improved adiabatic engine.
The present invention provides an internal combustion engine including:
a housing and piston means that are cyclically relatively displaceable along an axis to define a variable volume working chamber;
means to admit air and fuel to said working chamber for forming an ignitable mixture after compression of the air therein; and
means to exhaust combustion products from the working chamber;
wherein said variable volume working chamber includes at least two sub-chambers mutually displaced on said axis and in communication at a cross section at which gas in one sub-chamber may expand at least partially laterally as it flows from said one sub-chamber into the other sub-chamber;
wherein said air admission means, said exhaust means and said sub-chambers are arranged so that a swirl of gas is generated and maintained about said axis in both of said sub-chambers during operation of the engine;
and wherein said one sub-chamber is sealed and defined laterally and at an end by integral heat resistant and/or low thermal conductivity wall structure having a surrounding heat insulation jacket and associated heat dissipation means, arranged so that, during operation of the engine, the surfaces of the wall structure bounding said one sub-chamber are maintained at a temperature which is substantially higher than wall surfaces bounding said other sub-chamber.
Advantageously, said sub-chambers are arranged whereby the engine operates in a direct injection mode.
Said fuel admission means may include a fuel injector with a flow passage through said wall structure but preferably includes a fuel injector mounted intimately in a complementary opening or recess in said integral wall structure. The fuel injector preferably includes passages for cooling its tip.
The flow passage is advantageously arranged to open into said working chamber at a radius that divides the said one sub-chamber into a central cylindrical portion and an annular outer portion, which portions are of substantially equal volumes.
Said one sub-chamber is typically of mean width D and mean length L away from said cross-section where gas in one sub-chamber may expand at least partially laterally as it flows from said one sub-chamber into the other sub-chamber. The ratio L/D is preferably 0.9 or greater. In the simplest and most preferred case, said one sub-chamber is cylindrical, of diameter D and axial length L. Said cross-section is preferably equal to or less than said one sub-chamber.
Passages or galleries may be provided in a main cylinder of said housing extending about said other sub-chamber, for flowing lubricant therethrough, which lubricant is thereby effective to reduce or control temperatures and/or temperature differences across or around said cylinder, while being thereby heated to a desired functional viscosity.
The swirl of gas in said other sub-chamber is preferably such that there is formed therein a swirling cooler boundary layer, preferably effective to cool the peripheral and end walls of said other sub-chamber.
Preferably, the swirl of gas is such that the swirl ratio in said one sub-chamber is at least 6:1, and more preferably in the range from about 10:1 to about 25:1. In said other sub-chamber, the swirl ratio is preferably at least 3:1. The swirl of gas in said one chamber may be such that there is a radial temperature gradient in the gas flow of said one sub-chamber, with a relatively hotter core and a relatively cooler periphery.
In a preferred embodiment, the air admission means and the exhaust means include ports in said housing, and reciprocable sleeve valve means controlling the ports. Said one sub-chamber is then preferably disposed within junkhead means opposed to said piston means.
Preferably, the housing and ports are such as to allow no or minimal preheating of incoming air charges by hot combustion chamber walls.
Said housing may include respective cylindrical portions laterally defining said sub-chambers, and an annular shoulder between said cylindrical portions opposed to said piston means. The shoulder is preferably provided by an annular head member, and said heat dissipation means may include annular neck means bridged to said wall structure for reducing thermal conductance from the wall structure to the annular head member. Said shoulder and said neck means are advantageously formed integrally with said wall structure defining said one sub-chamber.
Preferably, in operation, the engine exhibits at least near adiabatic operation.
In an alternative embodiment, said one sub-chamber is substantially defined within said piston means.
Preferably, said sub-chambers are generally axially symmetrical about said axis, which is a longitudinal generally centre line axis of said housing.
The invention also provides, in a further aspect, an internal combustion engine including:
a housing and piston means that are cyclically relatively displaceable along an axis to define a variable volume working chamber;
means to admit air and fuel to said working chamber for forming an ignitable mixture after compression of the air therein; and
means to exhaust combustion products from the working chamber;
wherein said variable volume working chamber includes at least two sub-chambers mutually displaced on said axis and in communication at a cross section at which gas in one sub-chamber may expand at least partially laterally as it flows from said one sub-chamber into the other sub-chamber;
wherein said one sub-chamber is of mean width D and mean length L away from said cross-section, and the ratio L/D is 0.9 or greater; and
wherein said air admission means includes intake ports positioned and arranged to impart a swirl to gases in said chamber about said axis, including said laterally expanding gas flowing from said one sub-chamber into said other sub-chamber, whereby there is formed, during operation of the engine, a swirling cooler boundary layer in said other sub-chamber and a swirling flow in said one sub-chamber, the swirl ratio of said swirling flow in said one chamber being at least 6:1, preferably in the range 10:1 to 25:1.
The invention still further provides a method of operating an internal combustion engine at least near adiabatically, which engine has a housing and piston means defining a working chamber, the method including:
cyclically relatively displacing said housing and piston means along an axis to define a variable volume working chamber;
admitting air and fuel to said working chamber;
compressing the air in the working chamber to form an ignitable mixture;
causing combustion of the compressed air/fuel mixture;
exhausting gases from the working chamber including causing the gases to expand at least partially laterally as the gases flow from one sub-chamber of said working chamber into the other sub-chamber thereof; and
generating and maintaining a swirl of gas about said axis in both of said sub-chambers while the engine is operating;
wherein the wall surfaces bounding said one sub-chamber are maintained at a temperature which is substantially higher than wall surfaces bounding said other sub-chamber.
The ignitable mixture may be ignitable e.g. by compression ignition, or by spark or glow plug ignition. The air and fuel may be mixed in the working chamber, or partially or wholly externally of the chamber.
In general, the apparatus may perform a function other than as an engine, eg. a pump or compressor. More generally then, the invention provides a reciprocatory machine, including:
a housing and piston means that are cyclically relatively displaceable along an axis to define a variable volume working chamber;
means to admit fluid to said working chamber; and
means to exhaust fluid products from the working chamber;
wherein said variable volume working chamber includes at least two sub-chambers mutually displaced on said axis and in communication at a cross section at which gas in one sub-chamber may expand at least partially laterally as it flows from said one sub-chamber into the other sub-chamber;
wherein said fluid admission means, said exhaust means and said sub-chambers are arranged so that a swirl of fluid is generated and maintained about said axis in both of said sub-chambers during operation of the machine;
and wherein said one sub-chamber is defined laterally and at an end by a wall structure with associated heat dissipation means arranged so that, during operation of the machine, the surfaces of the wall structure bounding said one sub-chamber are maintained at a temperature which is substantially higher than wall surfaces bounding said other sub-chamber.
Any of the relevant preferred, advantageous and optional features set out above for the engine may also be included in the reciprocatory machine.